Induction cooking appliances or induction cookers are being ever more widely used. Their high efficiency and rapid reaction to a change of the cooking stage or level are advantageous. However, compared with glass ceramic hobs with radiant heaters, their disadvantage is the high price.
Induction cooking appliances normally comprise one or more induction heating devices with an induction coil associated with a given hotplate and which are subject to the action of an alternating voltage or alternating current, so that eddy currents are induced in a cooking utensil to be heated which is magnetically coupled with the induction coil. The eddy currents bring about a heating of the cooking utensil.
Numerous different circuit arrangements and drive methods are known for driving the induction coil. It is common to all the circuit and method variants that they generate a high frequency drive voltage for the induction coil from a low frequency input supply voltage. Such circuits are known as frequency converters.
For frequency converting or converting, normally the input supply or alternating supply voltage initially is rectified with the aid of a rectifier into a direct supply voltage or intermediate circuit voltage, and subsequently, for generating the high frequency drive voltage, processing takes place using one or more switching elements, generally insulated gate bipolar transistors (IGBTs). Normally a so-called intermediate circuit capacitor for buffering the intermediate circuit voltage is provided at the rectifier output, i.e. between the intermediate circuit voltage and a reference potential.
A converter variant widely used in Europe is a half-bridge circuit formed from two IGBTs, a series resonant circuit being formed by the induction coil and two capacitors, which are looped in serial manner between the intermediate circuit voltage and the reference potential. The induction coil is connected by one terminal to a connection point of the two capacitors and by another terminal to a connection point of the two IGBTs forming the half-bridge. This converter variant is efficient and reliable, but relatively expensive due to the two IGBTs required.
An optimized variant from the costs standpoint consequently uses a single switching element or IGBT, the induction coil and a capacitor forming a parallel resonant circuit. Between the output terminals of the rectifier, parallel to the intermediate circuit capacitor, are serially looped in the parallel resonant circuit of induction coil and capacitor and the IGBT. When operating this converter variant there is, however, a risk that under unfavourable operating conditions, e.g. when using an unfavourable cooking utensil, the components can become overloaded. This normally leads to a reduced service life of such induction heating devices.
The problem addressed by the invention is therefore to provide a method for operating an induction heating device, a method for saucepan detection for an induction heating device and an induction heating device, in which the induction heating devices have a frequency converter with a single switching element or IGBT and which in the case of changing operating conditions permit a reliable, component-protecting operation consistent with a long service life of the induction heating device.